Probably the most serious and intractable problems associated with the maintenance and operation of furnaces is the continuing necessity to maintain the interior furnace walls free of soot and other accumulated sediments which quickly build up and block the transfer of heat. This is particularly true with respect to coal fired boilers which have taken on a new importance in the face of dwindling supplies of oil and natural gas type fuels. Extremely heavy deposits of soot, ash, or slag can acccumulate on the interior walls of these furnaces producing very inefficient operation. The deposits can become so large and cumbersome that there is even a danger that they may fall off and physically damage the boiler.
In the prior art the solution to this problem has been to introduce through the furnace wall a large number of mechanically rotatable wall blowers sometimes called long-lance retracting blowers which rotate or oscillate. A high pressure cleaning fluid such as steam or air is directed through the lance onto the interior walls of the furnace in the hopes of blowing away the accumulated soot and ash. Mechanically rotated blowers have comparatively delicate mechanisms associated with them including driving gears and the various seals that convey the cleaning fluid through the rotating joints. Accordingly, the lance cannot be left in the furnace for long, but must be retracted, since it cannot endure the high operating temperatures therein. Normally, the lances are introduced periodically for a few minutes every hour or two and then withdrawn to protect their operating mechanisms. Hundreds of these lances may be required over the large surfaces of huge power plant boilers which are operated on a more or less continuous basis. Thus, this method of cleaning is extremely expensive, prone to frequent malfunction and failure, and cumbersome to operate. Furthermore, the resultant cleaning is not satisfactory since it can take place for only a small fraction of the time.